Horton

Re: PGPROC alignment (was Re: pgsql: Separate RecoveryConflictReasons from procsignals)

Peter Eisentraut <peter@eisentraut.org>

View thread View on postgr.es
From: Peter Eisentraut <peter@eisentraut.org>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Andres Freund <andres@anarazel.de>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2026-02-23T16:13:29Z
Lists: pgsql-hackers 
On 13.02.26 09:03, Bertrand Drouvot wrote:
> +/*
> + * If compiler understands aligned pragma, use it to align the struct at cache
> + * line boundaries.  This is just for performance, to (a) avoid false sharing
> + * and (b) to make the multiplication / division to convert between PGPROC *
> + * and ProcNumber be a little cheaper.
> + */
> +#if defined(pg_attribute_aligned)
> +                       pg_attribute_aligned(PG_CACHE_LINE_SIZE)
> +#endif
> +PGPROC;

You can/should use C11 standard alignas(), so you don't need to worry 
about whether it's supported or not.

Commits

  1. Use C11 alignas in typedef definitions

  2. Align PGPROC to cache line boundary

  3. Rearrange fields in PGPROC, for clarity

  4. Split PGPROC 'links' field into two, for clarity

  5. Remove useless store to local variable

  6. Separate RecoveryConflictReasons from procsignals